Clamp Settings for Getting Rid of Fireflies
First clamp cut the light value to the maximum you put so try first using hight values and then lowering from that as if you put it too low it will remove some light that is "real".

Second, you want to cut first the indirect light as it's normally what make more fireflies and direct light value is higher.

I recommend to start using a value of 100 or 10 in "clamp indirect", and reducing from it.